Particulate filters are used in vehicle exhaust systems to efficiently capture microscopic particles of soot, ash, metal, and other suspended matter which is generated during the fuel combustion process. However, over time the accumulated particulate matter increases the differential pressure across the filter. In order to extend the useful operating life of the filter and to further optimize engine performance, some particulate filters can be selectively regenerated using heat. Exhaust gas temperature is temporarily elevated by injecting and igniting fuel upstream of the filter above a calibrated light-off temperature. This process is often referred to as post-hydrocarbon injection or HCI.
In addition to the particulate filter, various catalysts may be used during the HCI process to further cleanse the exhaust gas. For example, palladium, platinum, or another suitable catalyst can work in conjunction with the regenerative heat to break down accumulated matter in the filter via a simple exothermic oxidation process. Additionally, the vehicle may use an exhaust gas recirculation (EGR) valve to direct a portion of the exhaust gas back into the engine's cylinders to further reduce vehicle emissions.
Within a turbocharged air intake compressor system, a variable geometry turbocharger, turbine, or other suitable device is driven by the exhaust gas that is discharged by the engine. The turbine rotates to drive an air compressor, which feeds the compressed intake air into the engine to boost engine power. Overall vehicle emissions performance is thus largely dependent on the temperature and mass flow of the exhaust gas and intake air at various stages of the combustion and exhaust cleaning processes.